Archwire assembly with non-linear crimpable orthodontic stop and method of manufacture

ABSTRACT

An archwire stop defines a non-linear path through the stop that results in a bend moment between an orthodontic stop and the portion of an orthodontic archwire passing through the stop. The bend moment is accommodated by elastic deformation of the archwire and stop, resulting in a predictable frictional engagement between the stop and the archwire that is useful in maintaining a stop mounted on an archwire during packaging, shipping and handling in a clinical setting. A non-linear path through an archwire stop may be created by a non-linear tubular stop or may be created by appropriate internal features of the stop. The non-linear path through the stop may be selected so that the frictional engagement is greatest toward the free ends of the archwire, preventing the stop from sliding off the ends of an archwire, while permitting adjustment of the stop at the front of the mouth during patient treatment.

BACKGROUND

The present disclosure relates to stops commonly used on orthodonticarchwires in combination with tooth-mounted orthodontic brackets fortreatment of tooth alignment issues. More particularly, the presentdisclosure relates to stops that define a non-linear path for anarchwire to minimize sliding on the archwire, archwire assembliesincorporating such stops pre threaded on the archwire and methods ofmanufacturing archwire assemblies incorporating such stops.

Orthodontic treatment normally involves the application of mechanicalforces to urge improperly positioned teeth into correct alignment. Onecommon form of orthodontic treatment includes the use of orthodonticbrackets that are fixed to teeth commonly by adhesively bonding thebrackets directly to the teeth. A resilient curved archwire is thenseated in the archwire slots of the brackets to impart mechanical forcesto the teeth via the bracket. In traditional orthodontic treatment, thearchwires may be secured to the brackets by ligature wires or elasticbands, which can limit relative movement between the archwire and thebrackets. It has been found that free movement of the archwire relativeto orthodontic brackets facilitates tooth movement, which is a goal oforthodontic treatment. Brackets of the self-ligating type were developedto eliminate the need for wires or elastic ligatures in securingarchwires to orthodontic brackets and permit greater freedom of relativemovement between the archwire and the brackets.

Brackets of the self-ligating type include a movable cover thatselectively closes the archwire slot of the brackets to secure thearchwire to the bracket, eliminating the need for ligature wires orelastic bands. The movable cover is opened for inserting the archwireand then closed for retaining the archwire within the archwire slot. Thearchwire is elastically deformed to engage the brackets, and seeks toreturn to its designed curve, thereby imparting mechanical force thaturges the teeth to move to the correct position over time. Once securedin the archwire slot by the cover, the archwire is free to movelaterally in the archwire slot, which facilitates tooth movement duringtreatment.

The enhanced freedom of movement of the archwire relative toself-ligating brackets can result in undesirable migration of thearchwire from its intended installed position. Unbalanced forcesproduced by the tongue, mouth muscles and chewing will move the archwirelaterally through the archwire slots of the brackets. This movement maycause a free end of the archwire to protrude from one of the bracketsattached to the molars and contact gum or cheek tissue. As a result ofthe movement, the opposite free end of the archwire may also becomedisengaged from its bracket. The protruding ends of the archwire canirritate the gum or cheek tissue. Further, orthodontic treatment isdisrupted by release of the archwires from the brackets.

Several conventional techniques are used to limit movement of thearchwire in the bracket slots to prevent disengagement of the archwirefrom the brackets as well as to direct forces to one or more teeth. Onetechnique is to insert the archwire through a crimpable sleeve, such asa small diameter tube, then position the archwire within the bracketslots with the sleeve located between two adjacent brackets. The sleeveis then secured (crimped) to the archwire at a fixed position to form astop. The sleeve is configured such that the sleeve cannot pass throughor move beyond an archwire slot as the archwire moves in the lateraldirection. In this manner, the maximum movement of archwire is limitedto somewhat less than the distance between the adjacent brackets. Thisarrangement effectively prevents the free ends of the archwire frombecoming disengaged from the molars at the back of the mouth whilepermitting free movement of the archwire relative to the bracket.

There are inherent complications with the use of stops in the clinicalsetting. The principle problem is their very small size. Typical stopsare about 10 to 30% of the size of an orthodontic bracket. Tubes usedfor stops are often 0.03″ to 0.04″ in diameter and only 0.08″ long.Tubes are mounted on the archwire in clinical settings such as adoctor's office, usually by the dentist or a dental assistant. It can bea challenge to see and handle these very small components, which thentend to slide freely along the archwire under their own weight. Thesesmall tubes may either slide to the wrong location for treatment orslide off the wire completely after being threaded onto the archwire butprior to installation being completed. A similar complication occurswhen the clinician uses multiple stops on a single wire and must controlthe stop location as the archwire is being placed in the patient'smouth. FIG. 2 illustrates a prior art stop mounted on an archwire, wherethe stop is free to slide along the archwire as described above.

It is known to provide assemblies with tubes (stops) that arepre-mounted on archwires. One common method is to deform (partiallycrimp) the stops against the archwire (also termed ‘flattening’) so asto limit the sliding motion and thereby prevent the stop from fallingoff of the archwire. Since archwires are typically curved in a flatplane, is intuitive to flatten the stop in a direction that is 90degrees to the plane P of the archwire as shown in FIG. 3. Theflattening method attempts to generate a sliding friction between thewire and stop by pressing the tube hard against the wire to create localwire-to-stop contact pressure across the width of the wire as shown inFIG. 4.

For the flattening process to work in a clinically acceptable manner, itis important to maintain a controlled amount of friction between thestop and the wire. Friction is generated by the clamping pressure of theflattened stop across the diameter of the wire as shown in FIG. 4.Though stop flattening is a simple concept, manufacturing experimentshave shown that the typical small variations in the dimensions of thewires and stops result in large variations in the friction of the stopson the wires. Large variations in friction result in some stops thateither fall off of the archwire or are too tight and cannot be movedeasily by the clinician. Other methods of deforming the stops such asnotching and pre-crimping (localized indentations as shown in FIG. 5),or partial crimping utilize the same general phenomena (pressure againstthe width of the wire) to produce local tube-to-wire friction at thesite of the notch or crimp and hence are subject to the sameunacceptably large variation in friction.

Another shortcoming of the flattening stop approach is that the frictionbetween the stop and wire changes as the stop is moved along the wire.This occurs because the sliding friction is generated by small contactareas between the stop and wire and these small contacts wear offquickly with a small amount of sliding. A stop with adequate initialfriction may lose that friction with clinical sliding adjustments.Increases in sliding friction have also been observed, which can becaused by slight increases in wire dimensions (because wire dimensionscan change locally within their tolerance range during productionprocesses). Also the stops themselves are often a soft metal and galling(soft metal smearing) can increase friction quickly. Fundamentally,these problems result from the reliance on contact pressure between stopand wire that is directed across the thickness dimensions of the wire.This contact pressure (and resulting friction) changes dramatically withsmall changes in dimensions in their zones of contact whether due tolocal wear or wire dimension changes.

There is a need for an improved archwire assembly that eliminates theneed for field assembly of stops onto an archwire. An additional need isthat a tube placed on the archwire will predictably remain in placeduring packaging, shipping and installation, but is easily moved to adesired position for final crimping.

SUMMARY OF THE DISCLOSURE

An archwire stop defines a non-linear path through the stop that resultsin frictional engagement between the archwire and the stop. Thenon-linear path through the stop is designed to create contact betweenthe archwire and the stop to impose a bend on the archwire as it passesthrough the stop. The term “bend” as used in this application issynonymous with “bend moment” and describes a situation of unbalancedcontact between the stop and archwire. Depending upon the structuralproperties of the archwire and corresponding stop, the stress of theresulting bend may be absorbed by reversible deformation (bending) ofthe archwire, the stop, or a combination of both. The dimensions andproperties of the stop and archwire may result in bending forces thatare difficult to measure, but are evident in the variable frictionalengagement between the stop and archwire at differently curved portionsof the archwire as described in greater detail below.

The bending force is resisted by the elastic nature of the archwire andstop and results in a predictable frictional engagement between the stopand the archwire that is useful in maintaining a stop mounted on anarchwire during packaging, shipping and handling in a clinical setting.A non-linear path through an archwire stop may be created by anon-linear tubular stop or may be created by appropriate internalfeatures of the stop. The non-linear path through the stop may beselected so that the frictional engagement is greatest toward the freeends of the archwire, preventing the stop from sliding off the ends ofan archwire. In some embodiments, frictional engagement is least towardthe center (anterior) of the archwire where the curvature of thearchwire most closely matches the bend imparted by the stop, makingrepositioning the stop straightforward during orthodontic treatment in aclinical setting. A variety of non-linear stop configurations willimpart the desired bend in an archwire and include curved, bent,dimpled, symmetrical and asymmetrical configurations.

There are several types of archwires used in orthodontic treatment.Common archwire materials include NiTi (Nickel Titanium), stainlesssteel and non-nickel containing wire material such as beta titanium.NiTi alloys may include between 1 to 10% Cu, Co, Nb, Pd or combinationsthereof. Nickel free Beta Titanium wires may include primary elements ofTi, Mo, Zr and 0-5% of additional elements selected from Sn, Al, Cr, V,and Nb or combinations thereof. Archwires are typically solid metal withcross sections that are round, square or rectangular. Other types ofwires are also used and these can include stranded and braided metalwires as well as newer polymer, plastic, ceramic and combinations ofthese materials. Nonmetallic materials may be combined with metallicmaterials to produce a composite archwire. Archwires constructed ofthese materials are designed to impart pre-determined mechanical forceson the brackets (and the associated teeth) through which they pass.Archwire materials exhibit significant elastic properties, permittingthem to be deformed to pass through misaligned tooth-mounted orthodonticbrackets and return to their pre-deformation shape, moving teeth in theprocess. As used in this application, the word “archwire” is intended toencompass orthodontic archwires without regard to the material fromwhich the archwires are constructed or their sectional configuration,whether solid, stranded, round, rectangular or square. Archwire, as usedin this application is expressly not limited to orthodontic archwiresconstructed of metallic wire materials.

Archwire stops are made in shapes compatible with the various archwiresand so are produced in circular, square, and rectangular cross sectionalshapes. Stops may be constructed of seamless tubing, welded tubing,split tubing, or slotted tubing, e.g., tubing that is discontinuous inits circumference. Tubular stops are typically fabricated from wroughtductile metal. Ductility is needed for the flattening, notching orcrimping deformation that is required to produce the wire-stop friction.Soft stainless steel is often used to construct orthodontic stops. Asthe tube material is typically softer than the metal wire, the processof deforming the tube is not expected to damage most metal wires.However, the flattening, crimping and notching processes for metal tubesare not expected to be compatible with non-metal wires. Orthodonticstops may include continuous round shapes, square shapes, rectangularshapes, more complex or random cross sectional shapes. Orthodontic stopsmay be constructed of other, non-metallic materials or metallicmaterials coated to resemble tooth color for aesthetic reasons. The word“stop” as used in this application is defined to encompass anorthodontic stop without regard to material or sectional configuration.The words “tubes” and “sleeves” are used interchangeably and are bothforms of an orthodontic “stop”.

Disclosed methods of manufacture include using a pair of dies to deformone or more stops while the stops are mounted on an archwire. Thearchwire supports the stop during forming to limit changes to thetubular cross section of the stop. The relatively elastic archwire isnot deformed, but the stop is deformed to a non-linear configurationwhich “grips” the archwire by forcing the archwire to bend slightly asit passes through the stop. The non-linear shape of the stop may beselected to impart a pre-determined frictional engagement between thestop and the archwire.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an archwire with two stops assembled on the archwire toform an archwire assembly;

FIG. 2 is an illustration of a common straight tubular stop on anorthodontic wire;

FIG. 3 illustrates a common prior art method of flattening a tubularstop on an archwire;

FIG. 4 is a cross section of a prior art flattened tubular stopillustrating the tube forces generating diametrical pressure on thearchwire;

FIG. 5 is a cross section of a prior art dimpled tubular stopillustrating the forces generated by the dimpled stop on the archwire;

FIG. 6 is an illustration of a non-linear tubular stop on an archwireaccording to aspects of the present disclosure;

FIG. 7 is a cross section of an archwire assembly incorporating anon-linear tubular stop illustrating the 3-point contact pattern thatgenerates a bending force on the archwire within the stop;

FIG. 8 is a perspective illustration of a method for forming anon-linear tubular stop and archwire assembly according to aspects ofthe disclosure;

FIG. 9 is a perspective illustration of an alternative method for anon-linear tubular stop and archwire assembly according to aspects ofthe present disclosure;

FIGS. 10 and 11 are schematic views of alternative non-linear stopconfigurations according to aspects of the present disclosure;

FIG. 12 is a schematic representation of a linear stop that defines anon-linear path for the archwire passing through the stop; and

FIG. 13 shows an archwire with two stops assembled on it about to beexposed to dies that will impart a non-linear configuration to thestops.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

Several embodiments of a non-linear configuration for crimpableorthodontic stops are disclosed. The term “non-linear” as used in thisapplication means “not straight” and is intended to encompass any stopconfiguration which imparts a bend (bending moment) to the archwirepassing through the stop. Points of contact 12 on the inside surface ofa stop 10 force an archwire 20 to bend when passing through the stop.Suitable features on the inside surface of a non-linear stop 10 may becreated without bending the entire stop, but may result from aparticular pattern of projections 14 toward a central axis of the stop10 c as shown in FIG. 12. An alternative approach is to bend all or partof the stop into a non-linear configuration, such as a curve of asuitable radius. Non-linear configurations specifically contemplated asfalling within the meaning of this term are illustrated in FIGS. 6, 7,and 10-12. A first embodiment is a design that uses lengthwise curvaturein a tube to produce reliable control of sliding friction on anarchwire. As shown in FIGS. 6 and 7, a non-linear stop 10 is mounted onan archwire 20. One or more non-linear stops 10 may be assembled on anarchwire to produce an archwire assembly 30 as shown in FIG. 1.

Stop sectional dimensions are selected to prevent movement into the slotof an orthodontic bracket. For this reason, the tube dimensions areintentionally larger than bracket slots they are used with. For example,a common orthodontic bracket slot width nominal dimensions are 0.018″and 0.022″ and stop outside diameter (O.D.) values for use with aparticular bracket will be larger than these slot dimensions, asdiscussed in greater detail below. Stops 10 are constructed from tubularmaterials defining a central passage chosen to slide on an archwire 20.As a result, the nominal inside diameter (or minor dimension for othershapes) will be somewhat larger than the diameter of archwires 20 withwhich the stops 10 will be used.

Non-linear stops create friction from the production of a bending momentbetween a length of the wire against at least a portion of the length ofthe tube (refer to FIGS. 7 and 10-12). The advantage of the bendingmoment is that it utilizes the inherent flexibility of the wire (and toa lesser extent, the stop) to generate a more predictable and repeatablesliding friction. The friction generated by a bending moment issignificantly less influenced by variation in the stop and wiresectional dimensions and is therefore inherently more predictable.Friction between a non-linear stop and an archwire is also less likelyto vary as a result of sliding the stop on the archwire duringinstallation or adjustment.

An added advantage of non-linear stops is that the design eliminates theproblem of tubes falling off the ends of the archwire. Archwires can bedescribed as having a shape that is similar to an inverted “U” as shownin FIG. 1. The anterior (front) portion 16 of an archwire 20 has greatercurvature than the posterior (rear) end portions 18. Another way todescribe the curvature of the archwire 20 is that it is defined by asmaller radius of curvature at the front (anterior) of the mouth and alarger radius of curvature toward the free ends 19 of the archwire 20which extend toward the molars at the rear (posterior) of the mouth.Archwire curvatures are not limited to circular curve portions based onone or more radii, and may include parabolic, elliptical and/or asphericcurved portions. Curvature descriptions that reference a radius ofcurvature are a convenient way of discussing the difference between thedesigned curvature of an archwire and the curvature of the archwireresulting from the bend moment imposed on the archwire as it passesthrough a non-linear stop. In the disclosed embodiments, the non-linearpath defined by the disclosed stops 10, 10 a, 10 b, 10 c is selected toimpart a bend having a radius of curvature less than the largest radiusof curvature on the archwire. This configuration ensures that, at theposterior regions (legs) 18 of the archwire having the largest radius ofcurvature, the stop 10, 10 a, 10 b, 10 c is configured to grip thearchwire 20 and not slide off. An alternative disclosed stop may beconfigured to impart a bend having a radius of curvature less than thesmallest radius of curvature on the archwire 20 to ensure at least somefrictional engagement between the stop 10 and archwire 20 even at thefront of the archwire (anterior portion 16), where the radius ofcurvature is typically the smallest.

It is important to note that while most orthodontic archwires are curvedin a flat plane P as shown in FIG. 1, other archwires have curvature intwo perpendicular planes. Such compound curved archwires are compatiblewith the disclosed non-linear stops and are intended to be encompassedby the term “archwire” as used in this application and the appendedclaims.

With the desired attributes of a non-linear path through the stop inmind, it is possible to calculate the dimensions and interior featuresof a stop that will impart a bend moment on the archwire 20 as it passesthrough the stop 10. Relevant variables are: the material, diameter,sectional shape and curvature of the archwire 20 as well as the insidediameter and length of the stop 10. For any given set of variables,there will be a minimum non-linearity required to ensure the stop 10imparts a bend moment to the archwire 20 as it passes through the stop10. Of particular relevance is the curvature of the archwire at theposterior (rear) portions 18, which may be referred to as “legs.” Anobjective of the non-linear path-induced bend moment is to ensure thestop 10, 10 a, 10 b, 10 c does not fall off the posterior free ends 19of the archwire 20. This requires a minimum frictional engagementbetween the archwire 20 and the stop 10, 10 a, 10 b, 10 c at least atthe posterior portions 18 of the archwire.

One benefit of certain embodiments of the disclosed non-linear stops 10is that the frictional engagement with the archwire 20 increases as thecurvature of the archwire decreases. This variable frictional engagementis most likely when the non-linearity of the stop occurs in the samedirection of curvature as the associated archwire 20. Stated anotherway, as the difference between the radius of curvature of the archwire20 (in a free state) and the radius of bend imparted by the stop 10increases, so does the frictional engagement between the stop 10 and thearchwire 20. This results in increased frictional engagement between thestop 10 and archwire 20 at the relatively straight rear (posterior)portions 18 (legs) of the archwire 20 and reduced frictional engagementon the anterior portion 16 of the archwire toward the front of themouth, where repositioning of the stop 10 on the archwire 20 isdesirable. Stops having the disclosed non-linear configuration areprevented from falling off the ends 19 of the archwire 20 and remainmoveable where needed by the practitioner. This design greatly minimizesthe possibility of accidental loss of stops 10 from the posteriorportion (rear leg 18/free ends 19) during handling and patienttreatment.

By contrast to the prior art flattened stop or partially crimped methodsthat produce frictional engagement at diametrically opposed points on anarchwire (see FIGS. 3-5), the disclosed non-linear stops 10, 10 a, 10 b,10 c are intentionally designed to produce a length-wise bend momentbetween the archwire 20 and the stop 10, 10 a, 10 b, 10 c as shown inFIGS. 7 and 10-12. The non-linear stop 10 results in contact with thearchwire 20 at longitudinally separated points 12 on the archwire 20 toimpart a bend moment in the archwire 20. The bending concept requires atleast three points of contact 12 between the stop 10 and the archwire20, with two of the points of contact 12 being separated by at least oneintermediate point of contact 12 a. The separated points of contact 12will be on an opposite side of the archwire from the intermediate pointor points 12 a, but no points of contact will be diametrically opposed.As shown in FIGS. 7 and 10-12, points of contact 12 between the stop 10,10 a, 10 b, 10 c and archwire 20 are defined by the non-linear stop andare substantially fixed with respect to each other. The bending momentimposed by the stop 10, 10 a, 10 b, 10 c is resisted by the elasticnature of the archwire 20, producing the predictable frictionalengagement. From FIGS. 7 and 10-12, it is clear that the points ofcontact 12, 12 a between the stop 10, 10 a, 10 b, 10 c and archwire 20are longitudinally separated and not diametrically opposed, as in theflattened or crimped tube approach show in FIGS. 4 and 5. Thisconfiguration reduces the influence of dimensional variation on thefrictional engagement between the stop and the archwire. One significantdifference between the prior art and the presently disclosed non-linearstops 10, 10 a, 10 b, 10 c is illustrated by comparing FIGS. 4 and 5(2-point contact/diametrically opposed) with FIGS. 7 and 10-12(multi-point contact/longitudinally separated/not diametricallyopposed).

Non-linear stops 10 according to the disclosure will produce a bendmoment contact load condition when used with an appropriate archwire 20.A non-linear stop 10 according to the disclosure will have at least 3substantially fixed points 12, 12 a on the inside surface of the stop10, 10 a, 10 b, 10 c arranged to be simultaneously in contact with thearchwire 20 with no 2 points of contact being diametrically opposed.Curved tube shapes that satisfy this requirement can be a simplelengthwise radius as shown in FIGS. 6 and 7 or a more complex shapecontaining compound radii or a tube with asymmetrical curve designs (notshown). FIGS. 10 and 11 illustrate non-linear stop configurations wherethe tubular stop 10 a, 10 b includes two or more straight segmentsarranged to provide the requisite points of contact 12, 12 a and bendingmoment on the archwire 20. FIG. 10 illustrates a bent tubular stop 10 awhere two segments of equal length meet at an obtuse angle selected toproduce the desired bend moment in the archwire 20. FIG. 11 illustratesa bent tubular stop 10 b where three segments meet at two obtuse angles.The non-linear stop 10 b of FIG. 11 has four points of contact with thearchwire, two on the inside of the archwire 12 a and two on the outsideof the archwire 12, with no two points of contact 12, 12 a beingdiametrically opposed to each other. The non-linear stop shapes 10, 10a, 10 b illustrated in FIGS. 7, 10 and 11 are symmetrical, but this isnot required. A curved or segmented stop may be asymmetrical and stillinclude the multiple points of contact 12, 12 a necessary to induce abend moment in the archwire 20 passing through the stop 10. A simpleexample would be the two segment stop of FIG. 10 where one segment islonger than the other. Curved shapes can be generated along the tubelength (inside and outside diameters) or on just the inside diameter.

One aspect of the disclosed non-linear stop is that the opening in theinterior passage defined by the stop, at any given point along the stop,exceeds the archwire cross sectional dimensions, while contact betweenthe wire at a minimum of three points on the inside surface of the stopgenerate an intentional bending moment between the stop and archwiresufficient to induce frictional engagement between the stop 10 and thearchwire 20. Note that it is intended that a bend moment impartedbetween the stop 10, 10 a, 10 b, 10 c and the archwire 20 is sufficientto create adequate friction but because the contact length of the stopis very short and the loads are low, these very local forces are notexpected to impart a bending force great enough to exceed the elasticrange of the archwire, which would distort the archwire from itsintended clinical shape.

Depending upon the dimensions of the archwire 20 and the correspondingstop 10, the bending moment may elastically deform the stop 10, thearchwire 20 or both. Whichever component deforms in response to thebending moment, a predictable frictional engagement between the stop 10and the archwire 20 is the result.

FIG. 12 illustrates an orthodontic stop defining a non-linear paththrough the stop 10 c, while the stop 10 c itself remains substantiallylinear. Dimples 14, 14 a project into the interior of the stop 10 c todefine three points of contact 12, 12 a the archwire 20 must pass on itsway through the stop 10 c. Two of the dimples 14 are on the same side ofthe stop 10 c, while the third dimple 14 a is located between the othertwo dimples 14 and on an opposite side of the stop 10 c. The threeprotrusions 14, 14 a into the interior of the stop 10 c impose a bendingmoment on the archwire 20 as it passes through the stop 10 c, generatinga predictable frictional engagement between the stop 10 c and thearchwire 20.

Non-linear configurations suitable for one archwire size may not besuitable for a significantly different wire size. Differently configuredarchwires may require stops with a specific non-linearity to produce anappropriate amount of friction (one curved tube may not work on all wiresizes). For rectangular wires (cross section width is different fromwire height) the orientation of the curved stop may change the amount offriction generated. In this case, the orientation of the stop will beimportant. Differently configured stops may be needed for wires withsignificantly different bending stiffness or surface finish properties(example, stainless steel vs. NiTi).

Stops are typically hollow, round ductile metal but other shapes arepossible. These shapes include hollow cross sections that are circular,elliptical, square, rectangular, or have more complex or irregulargeometries. Tubes for use as stops on orthodontic wires are commonlyproduced from a wrought, softened (annealed) stainless steel. But othertube production methods (casting for example) may be compatible with thedisclosed non-linear stops. Materials other than metal are compatiblewith the disclosed non-linear stops, but permanent fixation by meansother than crimping may be necessary (i.e. glue or heat bonding may workbetter with polymer tubes than crimping).

Methods of manufacture will be discussed with reference to the curvednon-linear stop 10 shown in FIG. 6. For purposes of discussion, thecurve induced in a tubular stop may be described by reference to asingle radius of curvature. A curve that is described by a radiusimplies a symmetrical bend or curve in the stop. The radius necessary toproduce a suitable friction generating bend in the archwire will be afunction of the wire size and curvature, tube I.D. size and tube length.There are several methods disclosed to produce a suitable curve orradius in a tube. One method is to press a selected tubular stop 10having a pre-determined length and cross sectional dimensions betweencurved dies 40 as shown in FIGS. 8 and 13. This can be accomplishedwhile the stop 10 is assembled on an archwire 20 or with the tubularstop independent of an archwire. The die pressing method of FIGS. 8 and13 may be compatible with the non-linear stop configurations shown inFIGS. 10 and 11. A second disclosed method is to apply a rolling orforming element 50 to one side of the stop 10 with the opposite side ofthe stop 10 placed against a shaped die 52, a rigid substrate, acompliant substrate or another forming or rolling element as shown inFIG. 9. All of these combinations can be used to create a curve in atube, and all can be used whether or not the tube is on a wire. Othermethods of forming will occur to those skilled in the art and all suchmethods may be compatible with the disclosed non-linear stops.

However, as noted previously, a curvature that is not a symmetricalcurve defined by a single radius may still function as intended for anon-linear stop according to the disclosure. Asymmetrical curves wherethe center of curvature is skewed toward one end or the other of thestop can provide the multipoint contact and bend moment as disclosedwith respect to symmetrical non-linear stops. The disclosed methods ofmanufacture may be applied to generate non-linear configurations thatare more complex than the simple non-linear configurations disclosed inFIGS. 7, 10 and 11.

Another approach to producing the disclosed non-linear stops is tomanufacture tubing with suitable curvature utilizing commercial tubeforming technologies. Individual tubes can be produced in this manner.Also, continuous or semi-continuous lengths having a desired non-linearconfiguration can be produced and cut to appropriate lengths.

Experimentation with fabrication of non-linear curved archwire stopsreveals that the disclosed stops generate predictable and repeatablefrictional engagement with an archwire. Experimentation has also proventhat acceptable frictional engagement between a non-linear orthodonticstop and the most common sizes and shapes of archwires can beaccomplished using only two sizes of stop material and two non-linearcurved configurations as follows. “Small” stops are suitable for usewith round wires 0.013″, 0.014″, 0.016″, and 0.018″ diameters. A smallstop is 0.080″ long, has an outside diameter (OD) of 0.032″ and aninside diameter (ID) of 0.020″. “Large” stops are suitable for use with0.016″, 0.018″ and 0.020″ square wires and 0.014″×0.025″, 0.016″×0.022″,0.016″×0.025″, 0.017″×0.025″, 0.018″×0.025″, and 0.019″×0.025″rectangular wires. Large stops are 0.080″ long, have an OD of 0.042″ andan ID of 0.032″.

Matching die sets were prepared to form small and large stops while thestops are threaded on one of the associated archwires as shown in FIG.13. Each die set includes a cylindrical male punch 40 a and a matchingfemale die block 40 b having a concave cylindrical surface opposed tothe male punch 40 a as shown in FIG. 13. The die set for the small tubesincludes a male punch with a forming surface radius measuring 0.710″ anda female die block defining a surface having a radius of 0.750″. The dieset for large tubes includes a male punch with a forming surfacemeasuring 0.960″ in radius and a female die block defining a surfacehaving a radius of 1.00″. Two stops 10 were threaded onto an archwire 20and placed between the male and female dies 40 a, 40 b as shown in FIG.13. The dies 40 a, 40 b are then closed on the archwire assembly atpredetermined pressures, which forms the stops 10 with a curvature thatimparts a bending moment as the archwire passes through the stop. Theresulting non-linear stops 10 were tested to see how much force wasrequired to move the stop 10 relative to the archwire 20 at both theposterior (rear legs) 18 and anterior (front) portion 16 of the archwire20.

Table 1 below shows the “minimum” die pressures that will form the stopsand result in acceptable average sliding force at the posterior (rear)portions of the respective archwires. A frictional engagement thatrequires approximately 0.5 lbs. of force directed along the length ofthe archwire is sufficient to prevent the stop from sliding off thearchwire during packaging, transport and patient care. So it is the lefthand column, showing the minimum frictional engagement with theposterior portions of the archwire, which is of significance in theminimum pressure scenario. It will be seen that the sliding forcerequired to move the stops on the anterior (front) portion of thearchwires is consistently lower than the sliding force required to movethe stop on the posterior (rear) portions of the archwire. Note theconsistency of the frictional engagement of the formed non-linear stopsat the anterior portion of the archwire as indicated by the standarddeviation.

TABLE 1 Die Pressure Ranges for Assembly of Tubes on Archwires Resultsfrom pressing values set at ‘minimum’ pressure Posterior Anterior DieAverage Average Pressure Tube Tube Wire Size (minimum) Tube SlidingSliding Wire Type Inches psi Die Set Size Force, lbs STDEV Force, lbsSTDEV Round 0.013 31 Small Small 0.5 0.17 0.3 0.04 0.014 31.0 SmallSmall 1.0 0.33 0.4 0.13 0.016 24.0 Small Small 0.6 0.16 0.3 0.14 0.01822.0 Small Small 0.6 0.22 0.2 0.02 Square 0.016 × 0.016 25.0 Large Large0.3 0.10 0.2 0.05 0.018 × 0.018 30.0 Large Large 0.5 0.36 0.2 0.03 0.020× 0.020 41.0 Large Large 0.4 0.25 0.1 0.03 Rectangle 0.014 × 0.025 41.0Large Large 0.5 0.19 0.2 0.01 0.016 × 0.022 30.0 Large Large 0.5 0.160.2 0.03 0.016 × 0.025 40.0 Large Large 0.7 0.36 0.2 0.09 0.017 × 0.02540.0 Large Large 0.5 0.20 0.2 0.01 0.018 × 0.025 40.0 Large Large 0.70.21 0.2 0.02 0.019 × 0.025 40.0 Large Large 0.8 0.35 0.2 0.04 Avg = 0.60.24 Avg = 0.2 0.05

Table 2 below shows experimental results for die pressures at valuesthat produce maximum acceptable frictional engagement between the stopand the anterior (front) portion of the archwire as shown in the righthand column. This frictional engagement cannot be so great as tointerfere with the clinical installation of the archwire assembly, whichrequires adjustment of the position of the stop along the archwire.Again, the frictional engagement with the anterior of the archwire issignificantly less than the frictional engagement with the posterior ofthe archwire.

TABLE 2 Results from pressing values set at ‘maximum’ pressure PosteriorAnterior Die Average Average Pressure Tube Tube Wire Size (maximum) TubeSliding Sliding Wire Type Inches psi Die Set Size Force, lbs STDEVForce, lbs STDEV Round 0.013 35.0 Small Small 0.8 0.22 0.5 0.2 0.01435.0 Small Small 1.1 0.43 0.7 0.4 0.016 30.0 Small Small 1.7 0.74 1.00.5 0.018 30.0 Small Small 1.6 0.48 0.4 0.1 Square 0.016 × 0.016 70.0Large Large 0.6 0.14 0.2 0.0 0.018 × 0.018 70.0 Large Large 0.8 0.41 0.20.0 0.020 × 0.020 70.0 Large Large 0.6 0.18 0.0 0.0 Rectangle 0.014 ×0.025 70.0 Large Large 1.3 0.58 0.8 0.4 0.016 × 0.022 70.0 Large Large0.9 0.65 0.3 0.0 0.016 × 0.025 70.0 Large Large 1.1 0.47 0.4 0.2 0.017 ×0.025 70.0 Large Large 0.9 0.50 0.2 0.0 0.018 × 0.025 70.0 Large Large0.9 0.24 0.3 0.1 0.019 × 0.025 70.0 Large Large 1.4 0.39 0.5 0.4 Avg =1.1 0.42 Avg = 0.4 0.2

These results demonstrate that predictable frictional engagement betweenan orthodontic stop and an archwire can be achieved by using thedisclosed methods to define a non-linear path through an orthodonticstop. The non-linear path creates points of contact inside the stop thatbend the archwire as it passes through the stop. The difference infrictional engagement with the posterior and anterior portions of thearchwire prove that the formed stops are non-linear and that thenon-linearity interacts with the curvature of the archwire to producesignificant and advantageous variation in the frictional engagementbetween the stop and the archwire. The results show that consistentlyuseful results are achievable using real world components and methods.Unexpectedly, all common wire sizes and shapes can be accommodated withjust two stop sizes and only two die sets, one for each size stop.

As shown in FIG. 12, the above discussed experiments were conducted withthe archwire positioned so that any non-linearity defined by the stopoccurs is in the same plane as the curvature of the archwire. With thenon-linear path through the stop in the same plane as the curvature ofthe archwire, the frictional engagement between the stop and thearchwire will vary according to the difference between the curvature ofthe archwire and the curvature of the bend moment imposed within thestop.

Aligning the curvature of the bend imposed by the stop results invariable frictional engagement, but such a relationship between thenon-linearity defined by the stop and the curvature of the archwire isnot mandatory. A stop defining a non-linear path for the archwire willalso produce useful and repeatable frictional engagement with thearchwire when the non-linearity defined by the stop is perpendicular tothe plane containing the curvature of the archwire. Such a stop wouldhave the same frictional engagement with the archwire along the entirelength of an archwire whose curvature is in a flat plane. The frictionalengagement would be selected to prevent the stop from falling off thearchwire during packaging, transport and clinical use, while alsopermitting easy adjustment during patient care. By varying theconfiguration of the non-linear path, the resulting bend imposed on thearchwire, and other variables, a suitable frictional engagement can becreated according to the disclosed methods.

It is anticipated that the disclosed non-linear stops can be useddirectly when field threading of tubes is indicated. Appropriate tubesizes will be required for the wire size that is used. It is alsoanticipated that pre-threaded tubes on wires will be sold as anassembly. Assemblies of tubes on wires can be generated by a number ofprocesses including by hand as well as by numerous semi- or fullyautomated processes.

What is claimed:
 1. An archwire assembly for orthodontic treatmentcomprising: a curved archwire including a length of elastic materialbetween two free ends and a curvature along said length, said length ofelastic material including an anterior portion, the curvature of saidanterior portion defined at least in part by a first radius ofcurvature, and a pair of posterior legs terminating at said free ends,the curvature of said posterior legs defined at least in part by asecond radius of curvature larger than said first radius of curvature;and a crimpable stop on said archwire and movable along the length ofsaid archwire, an inside surface of said crimpable stop including threepoints of contact with said archwire, two of said points of contactbeing longitudinally spaced along said archwire and one point of contactbeing intermediate said two of said points of contact, wherein contactbetween said crimpable stop and said archwire consists essentially ofsaid three points of contact, and said three points of contact impart abending moment having a third radius of curvature on a portion of saidposterior legs within said crimpable stop, said third radius ofcurvature smaller than said second radius of curvature, resulting infrictional engagement between said crimpable stop and said archwiresufficient to prevent said crimpable stop from moving on said posteriorlegs when exposed to a force equal to the weight of the crimpable stop.2. The archwire assembly of claim 1, wherein said archwire curvature isin a first plane and said bending moment is in said first plane and inthe direction of archwire curvature.
 3. The archwire assembly of claim1, wherein said archwire curvature is in a first plane, said crimpablestop is a non-linear tube having a curvature in the same plane as saidarchwire and the curvature of said crimpable stop is defined by a radiusless than any radius defining the curvature of said archwire.
 4. Thearchwire assembly of claim 1, wherein said two of said points of contactare on one side of said archwire and one of said points of contact is onthe opposite side of said archwire.
 5. The archwire assembly of claim 4,wherein said archwire curvature has an inside and an outside, said twoof said points of contact are on the outside of said archwire curvatureand one of said points of contact is on the inside of said archwirecurvature.
 6. The archwire assembly of claim 1, wherein said bendingmoment is in a plane perpendicular to a plane containing the curvatureof said archwire.
 7. The archwire assembly of claim 1, wherein saidcrimpable stop is a tube having open ends and an intermediate portionoffset relative to said ends in the direction of archwire curvature. 8.The archwire assembly of claim 1, wherein the frictional engagementbetween the crimpable stop and archwire varies according to thecurvature of the archwire, with frictional engagement between thecrimpable stop and the archwire increasing with the radius of curvatureof the archwire.
 9. The archwire assembly of claim 1, wherein saidarchwire is constructed of a solid metal wire or combination of metalwires in a stranded or braided configuration.
 10. The archwire of claim9, wherein said archwire is constructed of a superelastic metal alloyselected from the group consisting of NiTi, or NiTi containing 1 to 10%of Cu, Co, Nb, Pd or combinations thereof.
 11. The archwire of claim 9,wherein said archwire is constructed of a metal alloy selected from thegroup consisting of a Nickel-free Beta Titanium family of alloys withprimary elements of Ti, Mo, Zr, and 0-5% of an additional elements fromthe family Sn, Al, Cr, V, and Nb or combinations thereof.
 12. Thearchwire assembly of claim 1, wherein said archwire is constructed of anonmetallic material selected from the group consisting of plastic,polymer, ceramic and combinations thereof.
 13. The archwire assembly ofclaim 1, wherein the frictional engagement produced by said bendingmoment between the crimpable stop and archwire varies according to thecurvature of the archwire, with the bending moment and associatedfrictional engagement between the crimpable stop and the archwireincreasing with the difference between said third radius of curvatureand the curvature of the portion of the archwire within said crimpablestop.
 14. The archwire assembly of claim 1, wherein the crimpable stopis constructed of stainless steel or polymer material.
 15. The archwireassembly of claim 1, wherein said archwire is constructed of stainlesssteel.
 16. An archwire assembly for orthodontic treatment comprising: acurved archwire constructed from a unitary length of elastic materialextending between two free ends, said archwire curvature including afirst radius of curvature at a position substantially equidistant fromsaid free ends, a second radius of curvature larger than said firstradius of curvature adjacent said free ends and at least onetransitional curvature extending between said first radius and saidsecond radius; and a crimpable stop on said archwire and movable alongthe length of said archwire, an inside length of said crimpable stopdefined by a third radius of curvature smaller than said second radiusof curvature, said crimpable stop generating a bending moment on aportion of said archwire within said crimpable stop, resulting infrictional engagement between said crimpable stop and said archwiresufficient to prevent said crimpable stop from moving along the archwirepast said free ends when exposed to a force equal to the weight of thecrimpable stop.
 17. The archwire assembly of claim 16, said frictionalengagement being greatest on portions of said archwire having a largerradius of curvature and least on portions of said archwire having asmaller radius of curvature.
 18. The archwire assembly of claim 16,wherein said frictional engagement between said stop and said archwireincreases in proportion to the difference between the radius ofcurvature of said archwire and said third radius of curvature.